KR20010062560A - Position detection system for use in lithographic apparatus - Google Patents

Abstract

PURPOSE: A position detection system is provided to enable reference repeatable with a precision of mobile object, preferably, a submicrometer regarding to a reference frame. CONSTITUTION: The position detection system includes a radiation source(11) mounted on an isolated reference frame and a two-dimensional sensor mounted close to the radiation source(11). An object for positional detection is topped with a regressive reflector so as to reflect light radiated from the radiation source(11) along a return path which is in parallel with an incident light path but displaced from it. The quantity of displacement depends on the position of the object and is measured by the two-dimensional sensor. Such three devices are combined into a system to measure the position of the object at total six degrees of freedom.

Description

POSITION DETECTION SYSTEM FOR USE IN LITHOGRAPHIC APPARATUS}

The present invention relates to a position detection system that can be used to determine a reference position of a moving object. In particular, the present invention,

A projection system for supplying a projection beam of radiation;

A first object table for fixing patterning means capable of patterning the projection beam according to a predetermined pattern;

A second object table for fixing the substrate;

A projection system for imaging the patterned beam on a target area of the substrate; And

It relates to the use of the position detection system in a transfer projection device comprising a reference frame.

The term " patterning means " is to be broadly interpreted as meaning a means that can be used to provide an incident radiation beam having a patterned cross section corresponding to a pattern to be formed in a target area of the substrate, as used herein. Also used as the term "light valve". In general, the pattern will correspond to a particular functional layer in a device to be formed in the target area, such as an integrated circuit or other device (see below). Examples of such patterning means include the following.

A mask fixed by the first object table. The concept of masks is already well known in the lithography field, including masks of binary, alternating phase-shifted and attenuated phase-shifted masks, as well as various hybrid mask types. By placing such a mask in the projection beam area, selective transmission (in the case of a transmissive mask) or reflection (in the case of a reflective mask) of radiation incident on the mask is achieved according to the pattern of the mask. The first objective table ensures that the mask can be fixed at a predetermined position within the incident radiation beam area and, if necessary, should be able to move the mask relative to the beam.

A programmable mirror arrangement fixed by a structure (first object table). An example of such a device is a matrix-addressable surface with a viscoelastic control layer and a reflective surface. The basic principle of such a device is that (eg) the addressed area of the reflecting surface reflects incident light as diffracted light while the unaddressed area reflects incident light as non-diffracted light. Using a suitable filter, the non-diffracted light in the reflected beam can be filtered out leaving only the diffracted light. In this way, the beam is patterned according to the addressing pattern of the matrix-addressable surface. The required matrix addressing can be performed using any suitable electrical means. More information regarding such mirror arrangements can be obtained, for example, from US Pat. Nos. 5,296,891 and 5,523,193, which are incorporated herein by reference.

A programmable LCD arrangement fixed by a structure (first object table). An example of such a structure is in US Pat. No. 5,229,872, which is incorporated herein by reference.

For the purpose of simplicity of explanation, any of the remainder of this specification may, by itself, be referred to as an exemplary term including a mask. However, it can be seen that the general meaning of such an example is an extended concept of the patterning means described above.

The projection system will hereinafter be referred to as the "lens." However, the term should be interpreted broadly as encompassing various types of projection systems, including refractive optics, reflective optics, and catadioptric systems, for example. The floodlight system may also include components that operate according to any of the types of designs for directing, shaping, or controlling the emission of the projection beam, hereinafter collectively or individually. It may also be called a "lens." In addition, the first and second object tables may be referred to as "mask tables" and "substrate tables", respectively.

The transfer projection device can be used, for example, in the manufacture of integrated circuits (ICs). In this case, the mask (reticle) will comprise a circuit pattern corresponding to an individual layer of the integrated circuit, which pattern is then applied to a target area (silicon wafer) of one or more substrates coated with a layer of radiation sensing material (resist). Imaging with a die). In general, a single wafer has an overall network of adjacent target areas that are sequentially emitted one at a time through the projection system. Modern devices using a masking patterning method on a mask table can be divided into two different types of devices. In one embodiment of the transfer projection apparatus, each target region is radiated by exposing the entire reticle pattern onto the target region at once. Such an apparatus is commonly referred to as a wafer stepper. Alternatively, an alternative apparatus, commonly referred to as a step-and-scan apparatus, progressively scans the reticle pattern under a projection beam in a predetermined reference direction ("scanning" direction) while simultaneously scanning the reticle pattern. Each target area is radiated by scanning the wafer table in the same direction or in the opposite direction. In general, the projection system has a magnification factor M (usually < 1), so the speed V at which the wafer table is scanned is This is M times the speed at which the reticle table is scanned. More detailed information on the transfer device described herein can be found, for example, in US Pat. No. 6,046,792, which is incorporated herein by reference.

In general, an apparatus of this type has provided one first object (mask) table and one second object (substrate) table. However, devices are becoming available with at least two independently movable substrate tables. For reference, a multi-stage device is disclosed, for example, in US 5,969,441 and in US Application Serial No. 09 / 180,011 filed on Feb. 27, 1998 (WO 98/40791), which is incorporated herein by reference. . The basic operating principle of this multi-stage device allows the first substrate table to expose the first substrate placed on the table under the projection system, while at the same time the second substrate table is in the retracted position immediately after the exposure of the first substrate is completed. To take out the exposed substrate, pick up the new substrate again, perform an initial measurement of the new substrate, and then repeat the cycle of transferring the new substrate to the exposure position under the projection system and waiting. In this way, the throughput of the device can be substantially increased, thereby improving the maintenance cost of the device.

The size of the shape that can be imaged on the substrate in the transfer device is limited by the wavelength of the projection radiation. In order to produce integrated circuits with denser devices at faster working speeds, smaller shapes must be able to form. The most recent transcription projection devices use ultraviolet or excimer lasers generated by mercury lamps, but are projected radiation of electronics, for example higher frequency (energy) radiation such as extreme ultraviolet (EUV) or X-rays. Alternatively, for example, particle beams such as electrons or ions may be used.

In any type of transfer device, at any given point in time, the position of the movable part, such as the object table, must be accurately detected. Conventionally, this was measured using an incremental sensor such as an encoder or an interferometer to measure a change in position rather than detecting an absolute position. Thus, in order to provide a basis for using the extensibility positioning method for calculating the absolute position, it is necessary to additionally provide an origin reference sensor to detect when the movable object is at the reference point or the origin. Such origin reference systems may exhibit a repeatability of around 1 μm or slightly better.

In a positioning system of a substrate or mask, it is sometimes necessary to be able to position the mask or substrate with all six degrees of freedom (DOF). Accordingly, when six origin reference systems and six extendable positioning systems are combined together to be kinematically linked, reproducibility errors accumulate and exceed tolerance. Furthermore, sometimes the origin reference of the holder is held by a vibration-isolated reference frame and only the most important metrological components are mounted thereon. The origin reference of the encoder system for determining the approximate position is not suitable for this category and thus mounted on a separate structure, so its relative position to the insulated reference frame remains undefined in the micrometer class.

It is an object of the present invention to provide a referencing system which is capable of continuously detecting the position of a movable object relative to a reference frame, preferably with a precision of micrometer or less. Ideally, the system can position the moving object with six degrees of freedom at the same time.

1 is a view showing a transfer projection apparatus according to a first embodiment of the present invention,

2 is a plan view of a position detection system according to the present invention;

3 is a partial cross-sectional view of the position detection system of FIG.

4 is a cross-sectional view of a retro-reflector usable in the present invention;

5 is a cross-sectional view of an alternative retroreflector usable in the present invention.

According to the invention,

A projection system for supplying a projection beam of radiation;

A first object table for fixing patterning means capable of patterning the projection beam according to a predetermined pattern;

A second object table for fixing the substrate;

A projection system for imaging the patterned beam in a target region of a substrate; And

A transfer projection device comprising a reference frame,

A radiation source mounted to the reference frame;

A two-dimensional radiation detector mounted at a fixed position on the reference frame; And

And further comprising a position detection device comprising a mirroring device mounted to one of the objective tables relative to the reference frame to reflect the radiation emitted by the radiation source toward the radiation detector. There is provided a transfer projection apparatus characterized in that.

The position detector described above can measure the position of the object table in two degrees of freedom, and in order to detect the position of the table in six degrees of freedom, three such position detectors are arranged in different directions (i.e. Non-parallel), preferably in a substantially vertical direction.

The radiation source is preferably a collimated radiation source and includes a monochromatic light source such as a laser diode or LED mounted on the sensor housing or remote from the reference frame and is emitted from the light source by beam guide optics mounted on the reference frame. It may also be provided with an optical fiber for driving the light. The latter arrangement is advantageous because it not only removes potential heat sources that are very sensitive to temperature changes from the reference frame, but also increases collimated beam stability.

Two-dimensional position detectors are two-dimensional position sensing detectors (PSDs), CCD cameras, four quadrant photo-detectors, or output signals in two orthogonal respective directions as a function of the position of the reflected light beam. It can be any suitable two dimensional detector arrangement that can provide on the detector (array). The resolution of the CCD camera used in the present invention can be improved by sub-pixel interpolation.

According to another form of the invention,

A projection system for supplying a projection beam of radiation;

A first object table for fixing patterning means capable of patterning the projection beam according to a predetermined pattern;

A second object table for fixing the substrate;

Reference frame; And

A method of manufacturing a device using a transfer projection apparatus comprising a projection system for imaging the patterned beam on a target region of a substrate,

Providing a substrate having a radiation sensing layer formed thereon to the second object table;

Providing a projection beam of radiation using the projection system;

Using the patterning means to pattern a cross section of the projection beam; And

Projecting the patterned beam onto the target area of the substrate,

During or before the projecting step, emitting radiation from a radiation source mounted to the reference frame towards a mirror device mounted to one of the objective tables, reflecting the radiation by the mirror device; and Detecting the reflected radiation by a two-dimensional radiation detector mounted at a fixed position on the reference frame such that one of the objective tables relatively movable relative to the reference frame is determined to be at the reference position A method is provided.

In the manufacturing process using the transfer projection apparatus according to the present invention, the pattern of the mask is imaged on a substrate partially coated with an energy sensing material (resist) layer. Prior to this imaging step, the substrate is subjected to various procedures such as priming, resist application and soft bake. After exposure, the substrate will undergo another procedure such as post exposure bake (PEB), development, hard bake and measurement / inspection of the imaged shape. This series of procedures is used, for example, as the basis for patterning individual layers of IC devices. The patterned layer is then subjected to all the various processes for finishing individual layers such as etching, ion implantation (doping), metallization, oxidation, chemical-mechanical polishing, and the like. If several layers are required, the whole process or its modification process will be repeated for each new layer. In the end, an array of devices will be present on the substrate (wafer). These devices are separated from each other by techniques such as dicing or sawing so that each device can be mounted on a conveying device and connected to a pin. Further information on such a process can be obtained, for example, from "Microchip Fabrication: A Practical Guide to Semiconductor Processing (3rd edition, Peter van Zant, McGrawhill Publishers, 1997, ISBN 0-07-067250-4)". Can be.

In the use of the method and apparatus according to the present invention only reference is made to the fabrication of integrated circuits, it will be clearly understood that such apparatus has many other applications. For example, the apparatus may be used for manufacturing integrated optical systems, induction and detection patterns for magnetic region memories, liquid crystal display panels, thin film magnetic heads, and the like. Those skilled in the art, given the above-mentioned other applications, the terms "reticle", "wafer" or "die" as used herein are more general terms such as "mask", "substrate" and "target area" and the like. It will be understood that each can be replaced with.

As used herein, "radiation" and "beam" are terms used to encompass all forms of electromagnetic radiation or particle flux, and include ultraviolet (UV) radiation (e.g., 365 nm, 248 nm, 193 nm, 157 nm or Having a wavelength of 126 nm), extreme ultraviolet (EUV) radiation, X-rays, electrons and ions, and the like.

Hereinafter, the present invention will be described in more detail with reference to the accompanying schematic drawings and exemplary embodiments.

First embodiment

1 schematically shows a transfer projection apparatus according to the present invention. The device,

A radiation system LA, IL for supplying a radiation (e.g. UV or EUV radiation) projection beam PB;

A first object table (mask table) MT provided with a mask holder for fixing a mask MA (e.g., a reticle) and connected to first positioning means for accurately positioning the mask with respect to the item PL. ;

A second object table (substrate table) provided with a substrate holder for fixing the substrate W (e.g., a resist-coated silicon wafer) and connected to second positioning means for accurately positioning the substrate with respect to the item PL. ) (WT); And

A projection system (" lens ") PL (e.g., diffraction or catadioptric system, mirror group or field) that forms the irradiated portion of the mask MA on the target area C of the substrate W; Array of refractors).

As shown, the device is of a transmissive type (ie with a transmissive mask). In general, however, it may be reflective, for example.

In the illustratively shown figure, the radiation system is an undule provided around the path of the electron beam in a source LA (e.g., an Hg lamp, excimer laser, discharge plasma source, storage ring or synchrotron) that generates a radiation beam. An undulator or an electron or ion beam source). The beam travels along various optics (e.g., beam shaping optics Ex, integrator IN and condenser CO) included in the projection system, so that the final beam PB has a desired shape and Has an intensity distribution.

The beam PB passes through the mask MA, which is held in a mask holder on the mask table MT. The beam PB passing through the mask MA is focused while passing through the lens PL and directed to the target region C of the substrate W. With the aid of the interferometer displacement measuring means IF, the substrate table WT can be precisely moved such that, for example, the path of the beam PB is directed to another target area C. Similarly, after mechanically bringing the mask MA out of the mask library, for example, the first positioning means and the interference gauge displacement measuring means are used to accurately position the mask MA with respect to the path of the beam PB. Can be. In general, the movement of the objective tables MT, WT will be done with the help of a long stroke module (path positioning) and a short stroke module (fine positioning), although not clearly shown in FIG. .

The apparatus described above can be used in two different modes:

1. In the step mode, the mask table MT is necessarily kept fixed, and the entire mask image is projected to the target area C once (ie, a single “flash”). Subsequently, the substrate table WT may be shifted in the x and / or y directions so that another target region C may be radiated by the beam IB.

2. In the scan mode, the main scenario is the same as in the step mode, but the predetermined target area C is not exposed to a single "flash". Instead, the mask table MT is movable in a predetermined direction (so-called " scanning direction &quot;, for example, x direction) at a speed of v , so that the projection beam IB scans the mask image. Thus, the substrate table WT simultaneously moves in the same direction or in the opposite direction at the speed V = M v ; where M is the magnification of the lens PL, usually M = 1/4 or M = 1/5. In this way, a relatively large target area C can be exposed, regardless of the resolution.

2 is a plan view of an embodiment of the present invention used in conjunction with a substrate (wafer) table. It is clear that the present invention may be used with a mask (reticle) table. The wafer W and the reference X and Y axes are represented by virtual lines. The Z axis is perpendicular to the X and Y axes. The position detection system according to the present invention comprises three similar position detection devices 10A, 10B and 10C. Each position detection device comprises a radiation source for shooting an incident beam 12 of collimated radiation toward a retro-reflector 13, which is a reflector that reflects incident light in a parallel return path at a distance from the incident light path. 11). The displacement of the return beam 14 in two dimensions is a function of the relative position of the reflector and the radiation source in the plane perpendicular to the incident beam 12. The retroreflector 13 may consist of three mutually perpendicular planar reflectors which meet at one corner, for example, the so-called "corner cube". The reflector may be formed by mirror coating the three outer surfaces of the (virtual) corners cut from the reflective cube. The return beam 14 reaches the two-dimensional radiation detector 15.

The radiation source 11 and the radiation detector 15 are mounted adjacent to each other and also mounted in a very stable manner on an isolated reference or metrology frame MF of the transfer apparatus. For convenience, the radiation source 11 and the radiation detector 15 may be mounted on each other, or may be mounted on one bracket 16 as shown in FIG. The housing and / or mounting brackets of the position detector 15 and the radiation source 11 are preferably made of a material having a very low coefficient of thermal expansion such as Zerodur (RTM) or Invar for high thermal stability. The insulated reference or metrological frame MF can also be made of such a material. The retroreflector 13 may be mounted at a convenient point on the wafer table WT, for example near one corner.

The two-dimensional position detector 15 may be a two-dimensional position sensing detector (PSD), a CCD camera, four quadrant photodetectors, or any suitable two-dimensional detector arrangement, approximately perpendicular to the incident and reflected beams 12, 14. It is equipped with a sensing plane.

The positions of the position detection devices 10A, 10B, 10C and their orientations (ie, each α, β, γ) are selected to provide the most balanced position sensitivity possible in six degrees of freedom. In certain applications of the present invention, the position and orientation of the position detection device will be determined by factors such as the shape of the reference frame and the substrate table as well as the difference in sensitivity to position, pitch, roll, and yaw error of the transfer device.

3 is a partial sectional view of one position detection apparatus 10. As shown, the radiation source 11 and the radiation detector 15 are bracketed at positions where the incoming and return beams 12, 14 are inclined at an angle δ relative to the XY plane that is substantially parallel to the wafer W. It is mounted to the metrological frame MF via 16. Preferably, the angle δ is approximately 45E so that the horizontal and vertical displacement of the reflector 13 with respect to the incident light beam 12 of the same size results in the same displacement of the return beam 14 on the radiation detector 15.

As shown in FIG. 3, the radiation source 11 emits light onto the single mode optical fiber 112 so that the light can reach the collimating optics 113 mounted in the metrological frame MF (LED or laser diode). 111) or similar light sources. In this way, the light source 111 can be positioned away from the metrological frame MF and thermally insulated therefrom. The separation of the light source from the detector housing also results in very high pointing stability of the collimated beam to the sensor / detector.

4 shows the configuration of the corner cube reflector 13 inserted in the substrate table WT. In this case, the light source 11 shoots the incident beam 12 into the corner cube reflector 13 through the opening 17. The incident beam 12 is perpendicular to the upper surface of the substrate table WT and is reflected by the three faces 13a, 13b, 13c of the corner cube reflector 13 so that the return beam 14 is connected with the detector 15. It is on a parallel path. In this configuration, the position detection device detects the displacement in the direction parallel to the upper surface of the substrate table WT.

5 shows an alternative form of retroreflector 13N, known as 'cats-eye'. This can be used in place of the corner cube retro reflector 13. The 'cats-eye' 13N comprises a lens 131 and a mirror 132 spaced apart from the lens 131 by a distance equal to its focal length f. Conveniently, a lens is formed on the sculpted front surface of the single transparent body 133 having a flat back surface, optionally silver plated to form the mirror 132.

The three position detection apparatus of the present invention forming the position sensing system provides six signals according to the position and orientation of the wafer table WT. The system can be used in two modes:

-Origin detection system; The substrate holder is moved until all three detectors emit their home power in six degrees of freedom.

Positioning system; The sensor signal is converted into six degrees of freedom positioning information for an isolated reference frame as required by any servo or other controller by a control system (not shown) based on a suitable electronic or microprocessor. This can be done by sampling the sensor simultaneously or sequentially.

Ideally, the positions of the radiation source / detector unit on the metrological (reference) frame and the reflector on the table are determined so that the table can be moved to a position where the origin output is given for all six degrees of freedom at the same time (the "origin" position is The detectors do not need to be at their origin or median output, and any repeatable unique combination of output signals from three two-dimensional detectors can all be defined as the origin position). That is, the capture zones of all the detection devices 10A, 10B, and 10C should overlap. However, this configuration is not always possible due to the need for other components of the device. In such a case, each of the position signals from the incremental detector indicating the movement of the table between the specific positions indicated by the reference detection devices 10A, 10B, 10C used to determine the origin reference position, respectively. The table may be moved between the allocation areas of the apparatuses 10A, 10B, and 10C.

It should also be understood that the referencing process can be static or dynamic. In the static process, the table is moved to the reference position and then fixed while the required measurements are made. In a dynamic process that depends on sufficiently high sampling frequencies of the various sensors, the table is simply moved around or past the reference position, and the system's reference determination can be calculated through matching measurements from the absolute and extendable reference systems. . If the table does not actually pass the reference position or if the sample of the measuring system does not conform to the passage, the measured values can be extrapolated or interpolated as necessary.

The foregoing has only described the case where the present invention is used to detect the position of the substrate (wafer) table of the transfer apparatus. It will be readily understood that the present invention can also be used to detect the position of a mask (reticle) table of an electronic device or, in fact, any other movable object.

A distinct advantage of the position detection signal of the present invention is that there is no force remaining between the metrological (reference) frame and the wafer table as in the case of inductive, magnetic or capacitive sensors. This is important in that the reference or metrological frame is insulated with six degrees of freedom with extremely low natural frequencies for maximum stability. Any jamming force that may be transmitted to the frame by the sensor will cause vibrations with the coupling force, which will take a very long time to stabilize.

The second advantage is the use of straight light. This makes the sensitivity of the sensor almost independent of the working distance, which can give considerable flexibility to the layout of the reference frame, sensor module and objective table.

Although only described with respect to specific embodiments of the present invention, it will be understood that the present invention may be implemented in a manner different from that described. In particular, the present invention can be used to establish the origin reference of a metrological system for detecting the position of either a substrate (wafer) table or a mask (reticle) table in a transfer apparatus. Also, in transfer projection devices having multiple (substrate or mask) tables and / or multiple operating regions (e.g., exposure and measurement or characterization regions), such multiple systems may be provided at or near each working area. Static components (radiators and detectors) and reflectors for each table may be provided. Different sets of radiation sources and detectors may operate in conjunction with reflectors on any table that may be located within their operating area. The foregoing is not intended to limit the invention.

Claims (15)

A projection system for supplying a projection beam of radiation; A first object table for fixing patterning means capable of patterning the projection beam according to a predetermined pattern; A second object table for fixing the substrate; A projection system for imaging the patterned beam in a target region of a substrate; And A transfer projection device comprising a reference frame, A radiation source mounted on the reference frame; A two-dimensional radiation detector mounted at a fixed position on the reference frame; And And a position detection device having a mirror device mounted to one of the objective tables relatively movable with respect to the reference frame to reflect the radiation emitted by the radiation source toward the radiation detector. Transfer Projection Device. The method of claim 1, And the radiation source is a collimated radiation source. The method according to claim 1 or 2, And the radiation source is a monochrome radiation source. The method according to claim 1, 2 or 3, And the mirror device is a retro-reflector. The method according to any one of claims 1 to 4, And the radiation source comprises a light source mountable away from the reference frame, beam directing optics mountable on the reference frame, and optical fibers connecting the light source to the beam guidance optics. Device. The method according to any one of claims 1 to 5, And said radiation source comprises an LED or a laser diode as a light source. The method according to any one of claims 1 to 6, And the two-dimensional position detector is a two-dimensional PSD or CCD camera or four quadrant light detectors. The method according to any one of claims 1 to 7, And said retroreflector has a trapezoidal shape of material transparent to said radiation and has three mutually perpendicular surfaces which meet at one corner, said three surfaces having a reflective coating formed thereon. The method according to any one of claims 1 to 7, And said retroreflector comprises a converging lens and a reflective surface, said reflective surface being spaced from said lens by a focal length of said lens. The method according to any one of claims 1 to 9, Transfer projection device comprising a three position detection device formed therein. The method according to any one of claims 1 to 10, An extendable position sensing device for detecting the position of the movable object table in a detection area wider than the detection area of the position detecting device, and the position detector and the extendability for determining the absolute position of the object table in the detection area. And a means for combining the output signals from the position sensing device. A projection system for supplying a projection beam of radiation; A first object table for fixing patterning means capable of patterning the projection beam according to a predetermined pattern; A second object table for fixing the substrate; Reference frame; And A device manufacturing method using a transfer projection apparatus comprising a projection system for imaging the patterned beam on a target region of a substrate, Providing a substrate having a radiation sensing layer formed thereon to the second object table; Providing a projection beam of radiation using the projection system; Using the patterning means to pattern a cross section of the projection beam; And Projecting the patterned beam onto the target area of the substrate, During or before said projecting, emitting radiation from a radiation source mounted to said reference frame towards a mirror device mounted on one of said objective tables, reflecting said radiation by said mirror device and said reflection Detecting the detected radiation in a two-dimensional radiation detector mounted at a fixed position on the reference frame such that the objective table relatively movable relative to the reference frame is determined to be at a reference position. The method of claim 12, The transfer projection apparatus further includes an extendable position sensing system for sensing the position of the objective table, the method further comprising: after determining that the objective table is at the reference position, using the extendable position sensing system; Determining an absolute position of the objective table by measuring a movement of the objective table relative to a reference position. A device manufactured according to the method of claim 12 or 13. As a position detection device, A radiation source mounted on a reference frame; A two-dimensional radiation detector mounted at a fixed position on the reference frame; And And a mirror device mounted on an object relatively movable with respect to the reference frame to reflect radiation emitted from the radiation source toward the radiation detector.